Wet–dry seasonal and spatial variations in the δ 13C and δ 18O values of the modern endogenic travertine at Baishuitai, Yunnan, SW China and their paleoclimatic and paleoenvironmental implications

Abstract

Seasonal and spatial variations in the δ 13C and δ 18O values of the modern endogenic (thermogene) travertine deposited in a calcite-depositing canal at Baishuitai, Yunnan, SW China were examined to understand their potential for paleoclimatic and paleoenvironmental implications. The sampling sites were set in the upstream, middle reach and downstream of the canal, and the modern endogenic travertine samples were collected semimonthly to measure their δ 13C and δ 18O values. It was found that both δ 13C and δ 18O values of the endogenic travertine were low in the warm rainy season and high in the cold dry season, and correlated with each other. The low δ 18O values in warm rainy season were mainly related to the higher water temperature and the lower δ 18O values of rainwater, and the low δ 13C values are caused by the dilution effect of overland flow with low δ 13C values in the warm rainy season and the reduced CO 2-degassing of canal-water caused by the dilution effect of the overland flow. The linear negative correlation between the travertine δ 18O (or δ 13C) values and rainfall amount may be used for paleo-rainfall reconstruction if one knows the δ 18O (or δ 13C) values of the fossil endogenic travertine at Baishuitai though the reconstruction was not straightforward. It was also found that there was a progressive downstream increase of the δ 18O and δ 13C values of the travertine along the canal, the former being mainly due to the preferential evaporation of H 2 16O to the atmosphere and the latter to the preferential release of 12CO 2 to the atmosphere during CO 2-degassing. However, the downstream increase of the travertine δ 18O and δ 13C values was less intensive in rainy season because of the reduced evaporation and CO 2-degassing during the rainy season. To conclude, the downstream travertine sites could be more favorable for the paleo-rainfall reconstruction while the upstream travertine sites are more favorable for the paleo-temperature reconstruction. So, this study demonstrates that endogenic travertine, like epigenic (meteogene) tufa, could also be a good candidate for high-resolution paleoclimatic and paleoenvironmental reconstruction.